This invention relates to a photo-curable epoxy resin type composition. More particularly, it relates to a photo-curable epoxy resin type composition capable of giving a cured product which has shortened curing rate and improved curability and has electrical properties suitable for use in insulating materials for electrical equipments and also for use in resist materials.
Recent years, in view of energy saving and improvement of workability, attention has been paid to processes for curing resins by light. Of the processes, a process by which epoxy resins are cured by light has been applied widely and considered important. In the process for effecting photo-curing of the epoxy resins, most important factor is the epoxy resin composition itself, although the conditions for the photo-curing shall not be neglected, and extensive studies have been made on those having a variety of components. The photo-curable epoxy resin compositions having been known in the art can be roughly classified into the following two types.
One is a composition obtained by modification of an epoxy resin with use of a vinyl group-containing compound such as an acrylic acid and its derivatives However, a photo-cured product of the modified epoxy resin has a problem that it is considerably inferior to a cured product of the epoxy resin itself in the heat resisting property.
The other is a composition obtained by adding to the epoxy resin a photodecomposable type catalyst and curing it by use of the catalyst An example of the catalyst used therefor is a complex represented by the following formula: ##STR1## wherein Ar represents a phenyl group, or the like; X represents an iodine atom, a sulfur atom, a diazo group, or the like; and Y represents BF.sub.4, PF.sub.6, AsF.sub.6, SbF.sub.6 or the like,
as disclosed in Macromolecules, 10, 1307 (1977); Journal of Radiation Curing, 5, 2 (1978); Journal of Polymer Science Polymer Chemistry Edition, 17, 2877 (1979); ditto, 17, 1047 (1979); Journal of Polymer Science Polymer Letters Edition 17, 759 (1979); Specification of Japanese Unexamined Patent Publication (KOKAI) No. 65219/1980; specification of U.S. Pat. No. 4,069,054; specification of British Patent No. 1,516,511; specification of British Patent No. 1,518,141; etc.
However, when the composition obtained by adding to an epoxy resin the photo-curable type catalyst is used, the resultant photo-cured product has a good mechanical strength and a heat resisting property, whereas the catalyst component tends to remain as an ionic impurity. Therefore, it has problems that the deterioration of electrical properties such as electrical insulating property and corrosion phenomenon in electrical equipments may occur when such a cured product is applied in an electrical equipment.